11 
few days lie informed me that the mulberry-tree sap was 
of a milky nature, and did actually contain caoutchouc, 
especially on dry and bright sunny days. 
With respect to the Geographical distribution of Plants, 
especially in its connexion with Climate, I wish to say 
a few words, in order to shew that the argument I after- 
wards draw from it, is based on a sure foundation. In 
repeating nearly what I have said elsewhere, I shall 
confine myself to the more marked differences of climate, 
and the vegetation it supports. 
The peculiarities of the tropical zone we well know to 
be brightness of light, great heat, and moisture, with 
considerable uniformity of all throughout the year. These 
are all favourable to the development of vegetation, whicn 
is accordingly characterised by vastness ; the foliage, by 
richness ; and the inflorescence, by brilliancy of colouring. 
Hence, the proportion of trees is great, and their flowers 
of a size and richness which, in colder climates, are only 
the appanage of humbler plants ; as may be seen in the 
noble Amherstia, the wide-spreading Bombax, or glowing 
Erythrina. If we study the physiology of plants, as well 
as the circumstances controlling their growth, and the 
nature of their secretions, we find that vegetation is much 
affected by the different physical states of the soil and 
atmosphere, as well as by the supply of heat and light ; 
hence we may conclude, that there are different sets of 
plants fitted by nature for the particular circumstances in 
which they are to be placed. Those who have visited 
tropical countries, know that the position of their low and 
mangrove-lined coasts may be recognised by the forests of 
tall palms, shooting like distant masts above the surface of 
the sea. The very mention of the Clove, the Cinnamon, 
Nutmeg, Ginger, Cardamom, Plantain and Pepper recall 
ideas of high .temperature and rich vegetation : but these 
all belong to separate families of plants, as Myrtacece, 
c2 
